The answer to this question is attempted by the theory of atoms: the doctrine which teaches that the whole material world is composed of simple particles which are no farther divisible, and from whose juxtaposition the chemical elements--and, in respect to their other forms of existence and combination, the whole world of bodies, with all their forms, states, and changes,--are composed. This theory has not only the practical value that the physical (and especially the chemical) sciences can make and use their formulas most easily under the supposition of such simple primitive elements; but it also has the great theoretical merit that it has broken down the old barriers between _matter_ and _force_, and has thus promoted considerably our method of regarding the world of material substances. Toward this result, scientists and philosophers--and, among the latter, the thinkers and investigators of both views of the world, the theistic and the pantheistic, the ideal and the materialistic,--have worked with equal merit, and have equally enjoyed its fruits, with perhaps the single exception of so pure a materialist as Ludwig Buechner, who, it seems, does not like to give up his old doctrine of force _and_ matter as the two inseparable, equivalent, and equally eternal elements of the universe. That matter itself, even when looked upon from a purely physical standpoint, has an incorporeal principle; that the whole world of bodies, as such, has but a phenomenal character; that not force _and_ matter are the two empirico-physical principles of the world, but that matter itself must be a product of elementary {142} force active in the atoms; these doctrines have now be pretty nearly common property of natural science and philosophy. Investigators who like Wilhelm Wundt, rise from natural science to philosophy, or such as take their starting-point from philosophy--whether they be theists, like Lotze, I. H. Fichte, Ulrici, or occupy the ground of a pessimistic pantheism, as does Eduard von Hartmann,--all share this view and its fruits. But in spite of all these preferences for the theory of atoms, we should not forget that it still has but hypothetical value--that it is but an idea of limits, which indicates, where the scientifically perceptible ceases, and that every attempt at moving this limit still farther on must either fail and lead into unsolvable contradictions, or, if successful, only leads to new difficulties and unsolved problems.